Volume 14, Number 3, Sept 1992, pp.28-29, illustrations
In summer 1991, we had something rather rare happen in Colorado: heavy rains. After one such rainstorm, on a Friday evening after closing, the roof of the Rocky Mountain Conservation Center leaked. Although the roof did not leak directly over any artifacts, a puddle on the floor caused the humidity in the lab to spike from 55% to 75%, staying at 75% for 3 days before the situation was discovered.
At the time, we had in the lab two large flags mounted on paper honeycomb panels. For each, an attached plexiglas cover, or vitrine, protected the side on which the flag was mounted. When we checked the panels for damage after the roof leak, we saw that they had distorted due to the humidity fluctuations.
After the flags were removed from the honeycomb panels, we discovered that the fronts of the panels were actually more damaged than the backs, which had been directly exposed to the high-humidity environment. The panels had "self-destructed" from shrinkage and expansion, combined with adhesive failure within their corrugated structure.
There are, in fact, numerous problems with acid-free paper honeycomb panels as support for oversize flat textiles:
Acknowledging these shortcomings, we decided to look for a replacement material.
To begin with, a custom stretcher of the type used by our paintings department would be fully adjustable, differing from the wooden frame used in conjunction with the honeycomb panels. This would enable us to fit the mount more closely into the vitrine. The problem then was to find a suitable barrier material. The solid backing is not for support, but serves as an environmental barrier. We considered Fomecor, but we were concerned about the eventual degradation of the foam filling.
Corrulite, a high-density polyethylene (HDPE), was considered next. However, several construction problems needed to be addressed:
Using the HDPE panel in conjunction with a wooden stretcher, however, solves all these problems.
Upper: cross section of 1/8-in. Corrulite panel
Lower: cross section of 1/8-in. Coroplast panel
We contacted the Corrulite Company and determined that the 165# weight panels would be suitable for our purposes. Our only problem was the high per-panel cost due to shipping charges: four panels would cost $50 each. I found a local distributor, however, that supplies a similar product called Coroplast for about $9 per panel. Corrulite is a laminated board, while Coroplast is a profile extrusion. Both types seem to be equally strong.
High-density polyethylene panels have many advantages over paper honeycomb panels:
Since HDPE is a non-hygroscopic material and the panel can be fitted tightly into the vitrine cover, there was concern that under certain conditions, condensation could form on the inside of the vitrine cover. An experiment was performed to simulate these conditions. A 16-inch x 22inch panel was constructed in the same manner as a full-sized one. Linen fabric was stretched over this panel and stapled to the back of the wooden stretcher using copper staples. This panel was fitted snugly inside its vitrine, leaving a total internal volume measuring 748 cubic inches. A humidity indicator strip was placed between the panel and the vitrine, and another was placed outside it. The vitrine and panel assembly was laid flat inside a humidity chamber on two braces to simulate the air flow in a display or storage situation. The ambient humidity at the outset of the experiment was 35%. Humidity was introduced into the chamber using two 1000-ml beakers of hot water, and the chamber was sealed. Within 12 hours, the humidity in the chamber had reached 100%, and while there was condensation on the walls and top of the chamber itself, there was none on or inside the vitrine. The humidity inside the vitrine at this time remained at 35%-40%. It took four days in a humidity of 100% to raise the humidity within the vitrine to 80%. The external humidity was kept at 100% for another four days, but the internal humidity never rose above 80%. Next, the top of the humidity chamber was removed and the external humidity dropped from 100% to 35% in a matter of minutes. It took six days for the vitrine's internal humidity to match the exterior level.
There was no condensation on the inside of the vitrine at any time during the experiment. The experiment showed that HDPE panels provide an effective water vapor barrier. During this test, neither the copper staples nor the zinc screws corroded, and the linen showed no corrugation imprints upon removal from the panel.
We have concluded that high density polyethylene panels offer many advantages over paper honeycomb panels in the construction of textile mounts. The HDPE panels provide a buffer to humidity changes, they are chemically inert, they require about half the time to construct, and they are less expensive. Even using the more expensive adjustable stretcher frame, the total cost for mount supplies using HDPE panels is about 75% of the cost of materials for a paper honeycomb panel mount.
This new method has been adopted by the Rocky Mountain Conservation Center for oversized textiles mounted in vitrines. As with all large mounts with plexiglas vitrines, the mount assemblage should be stored vertically to prevent stress fracture to the plexiglas sheet on the front.Elizabeth M. Red Elk
Construction of recommended support
for oversized flat textiles
Timestamp: Thursday, 11-Dec-2008 13:02:30 PST
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